The present invention generally relates to a vacuum cleaner and a method of control thereof. More specifically, the present invention relates to a vacuum cleaner using a power brush suction port provided with a rotary brush, which vacuum cleaner is operated under an optimum state according to a control method which depends upon a characteristic of the floor surface to be cleaned and the suction port under use.
In the conventional vacuum cleaner, as described in JP-A-64-52430, the sorts of surface to be cleaned are sensed from a variation in a current flowing through the nozzle motor mounted on the air suction port, and the input to the fan motor is controlled based on this result.
According to the above-described vacuum cleaner, the current flowing through the nozzle motor mounted on the suction port will vary depending upon the operators using the vacuum cleaner. Thus, there is a problem in such a method for sensing the sorts of floor surfaces in response to the current values in that the sorts of floor may be mistakenly judged.
As a conventional vacuum cleaner, another type of vacuum cleaner has been described in JP-A-63-309232, in which, when the value of the current flowing through the nozzle motor provided at the suction port exceeds a certain setting value for more than a certain setting time period, the supply to the nozzle motor is turned OFF.
In the conventional techniques, since the current flowing through the nozzle motor provided at the suction port will vary depending upon the operators using the vacuum cleaner, and also the magnitudes thereof may vary depending upon the sorts of cleaning surfaces, there are many possibilities to judge that the rotary brush is locked, depending upon the current setting value and the setting time period. Conversely, if the values of the current setting value and setting time period are set too large, there is another problem in that the motor may be damaged.
Furthermore, there has been disclosed a conventional method in JP-A-63-65835, in which the suction force of the vacuum cleaner is sensed by a sensor in order that the vacuum cleaner may be automatically operated so as to improve operabilities thereof and save power consumption. However, as objects to be sensed by this sensor are the static pressure within the main body of the vacuum cleaner and the air capacity, it is difficult to properly judge the conditions of the cleaning surfaces based upon only this sensed object. Also in the automatic control operation, the shapes of the suction characteristic diagram represented by the static pressure and air quantity are adjusted and the vacuum cleaner is operated in accordance with the determined static pressure/air quantity characteristic. Accordingly, it is rather difficult to control the vacuum cleaner at the optimum state, depending upon the sorts of cleaning surfaces and also suction ports, as well as the states of use of the vacuum cleaner.
In another conventional vacuum cleaner, the AC commutator motor is employed as the driving source and a triac is combined with the pressure sensor or air quantity (capacity) sensor; the voltage applied to the AC commutator motor is controlled or adjusted by way of the triac; and then the power to the vacuum cleaner is controlled, depending upon the surfaces to be cleaned, or the pressure sensor or air quantity sensor.
In this conventional vacuum cleaner, the various factors indicative of the load conditions of the fan motor, namely the air quantity are directly sensed by the air-quantity sensor, otherwise the relationship between the static pressure and air capacity has been previously stored as the memory table, whereby the static pressures are sensed from the output from the pressure sensor in order to control the rotational speed. As a consequence, there are such problems that higher cost is required to mount the pressure sensor and a large volume is required in the former case, and furthermore, if the air quantity is required at high precision over a wide range, a huge amount of table data is necessarily required.